How to choose between the past and present of MOS tube and IGBT tube?

In Electronic circuits, MOS tubes and IGBT tubes often appear, and they can be used as switching elements. MOS tubes and IGBT tubes are similar in appearance and characteristic parameters, so why do some circuits use MOS tubes? And some circuits use IGBT tubes?

In electronic circuits, MOS tubes and IGBT tubes often appear, and they can be used as switching elements. MOS tubes and IGBT tubes are similar in appearance and characteristic parameters, so why do some circuits use MOS tubes? And some circuits use IGBT tubes?

Let’s take a look at the difference between MOS tube and IGBT tube!

How to choose between the past and present of MOS tube and IGBT tube?  

What is a MOS tube?

There are two main types of field effect transistors, namely junction field effect transistor (JFET) and insulated gate field effect transistor (MOS tube).

MOS tube is MOSFET. The full Chinese name is metal-oxide semiconductor field effect transistor. Because the gate of this field effect tube is isolated by an insulating layer, it is also called an insulated gate field effect tube.

MOSFET can be divided into N-channel depletion mode and enhancement mode; P-channel depletion mode and enhancement mode.

How to choose between the past and present of MOS tube and IGBT tube?

▲ MOSFET types and circuit symbols

Some MOSFETs have a diode inside, which is a body diode, or a parasitic diode or a freewheeling diode.

How to choose between the past and present of MOS tube and IGBT tube?

There are two explanations for the role of parasitic diodes:

1. The parasitic diode of the MOSFET is used to prevent the MOSFET from burning out when the VDD is over-voltage, because before the over-voltage causes damage to the MOSFET, the diode first reverses breakdown and directs the large current to the ground, thereby avoiding the MOS The pipe was burned out.

2. Prevent the MOS tube from burning out when the source and drain of the MOS tube are reversely connected. It can also provide a path for the reverse induced voltage when the circuit has a reverse induced voltage to avoid the breakdown of the MOS tube by the reverse induced voltage. .

MOSFET has the characteristics of high input impedance, fast switching speed, good thermal stability, and voltage control current. In the circuit, it can be used as an amplifier, electronic switch and other purposes.

What is IGBT?

IGBT (Insulated Gate Bipolar Transistor), an insulated gate bipolar transistor, is a compound semiconductor device composed of a transistor and a MOS tube.

As a new electronic semiconductor device, IGBT has the characteristics of high input impedance, low voltage control power consumption, simple control circuit, high voltage resistance, and large current. It has been widely used in various electronic circuits.

The circuit symbols of IGBTs have not been unified so far. The symbols of transistors and MOS tubes are generally used when drawing schematic diagrams. At this time, it is possible to judge whether it is IGBT or MOS tube from the model marked on the schematic diagram.

At the same time, pay attention to whether the IGBT has a body diode. The fact that it is not marked on the figure does not mean that it does not exist. Unless the official information specifically states, this diode is present.

How to choose between the past and present of MOS tube and IGBT tube? 

The body diode inside the IGBT is not parasitic, but is specially set to protect the fragile reverse withstand voltage of the IGBT. It is also called FWD (Freewheeling Diode).

It is not difficult to judge whether there is a body diode inside the IGBT. You can use a multimeter to measure the C pole and E pole of the IGBT. If the IGBT is good and the measured resistance values ​​of the C and E poles are infinite, it means that the IGBT does not have a body diode.

IGBT is very suitable for applications such as AC motors, frequency converters, switching power supplies, lighting circuits, traction drives and other fields.

Structural characteristics of MOS tube and IGBT

The internal structure of MOS tube and IGBT tube is shown in the figure below.

How to choose between the past and present of MOS tube and IGBT tube?

The IGBT is constructed by adding a layer on the drain of the MOSFET.

The ideal equivalent circuit of IGBT is shown in the figure below. IGBT is actually a combination of MOSFET and transistor. MOSFET has the shortcoming of high on-resistance, but IGBT overcomes this shortcoming, and IGBT still has low on-resistance at high voltage. .

How to choose between the past and present of MOS tube and IGBT tube?

In addition, for IGBTs and MOSFETs with similar power capacities, the speed of IGBTs may be slower than that of MOSFETs, because IGBTs have a turn-off tail time. Due to the long turn-off tail time of IGBTs, the dead time will be longer, which will affect the switching frequency.

Choose MOS tube or IGBT?

In the circuit, whether to choose a MOS tube as a power switch tube or an IGBT tube is a problem that engineers often encounter. If considering the system voltage, current, switching power and other factors, the following points can be summarized:

How to choose between the past and present of MOS tube and IGBT tube?

You can also see the conditions of use of both from the following figure. The shaded area indicates that both MOSFET and IGBT can be used. “?” indicates a level that cannot be reached by the current process.

How to choose between the past and present of MOS tube and IGBT tube?

In general, the advantage of MOSFET is that it has good high-frequency characteristics, and its operating frequency can reach hundreds of kHz or up to MHz. The disadvantage is that the on-resistance is large in high-voltage and high-current situations. It has excellent performance under the condition of low on-resistance and high withstand voltage.

MOSFETs are used in switching power supplies, ballasts, high-frequency induction heating, high-frequency inverter welding machines, communication power supplies, and other high-frequency power supplies; IGBTs are concentrated Audio induction heating and other fields.

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